1. Field of the Invention
The present invention relates to an optical fiber array and a manufacturing method thereof.
2. Description of the Related Art
In recent years, optical fibers have become a focus of attention especially in a communication field. Particularly, in the field of IT (information technology), a communication technology using the optical fibers is required for improvement of a high speed Internet network.
The optical fiber has characteristics of low loss, high band, thin diameter, light weight, noninductivity, resource saving, and the like. Therefore, in a communication system using such optical fiber, the number of repeaters can largely be reduced and construction and maintenance can be facilitated as compared with a communication system using a conventional metallic cable. As a result, cost efficiency and reliability of the communication system can be enhanced.
The optical fiber can not only transmit light of one wavelength, but also transmit light having many different wavelengths at the same time with one optical fiber in a multiplex manner. Therefore, it is possible to realize a large-capacity transmission which is applicable to a wide range of uses, and there is a great merit that the optical fiber can be used for video services and the like.
In an optical communication using the optical fiber, an optical fiber ribbon in which a plurality of optical fibers are disposed in parallel and covered with a resin layer is used. An optical fiber array in which a plurality of optical fibers are aligned at predetermined distances from one another is usually used for connecting the optical fiber ribbon with light receiving elements, light emitting elements, and various terminal equipment (such as a personal computer, a mobile device, and a game). The optical fiber array is formed by removing the coating resin layer of an end of the optical fiber ribbon, exposing ends of the optical fibers, disposing and fixing the exposed optical fibers in V-grooves of a substrate, and mounting a lid for covering the exposed optical fibers on the substrate by an adhesive layer.
Such an optical fiber array is manufactured in the following manner as disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-181724. A V-groove substrate is provided with a plurality of V-grooves for positioning optical fibers by which a plurality of optical fibers are disposed in parallel. A plurality of optical fibers are disposed in parallel on the V-groove substrate such that tip ends of the optical fibers project from an end surface of the V-groove substrate. Next, a lid is placed on an opening side (upper side) of the V-groove substrate, and the optical fibers are sandwiched between the V-groove substrate and the lid. Then, adhesive is applied to the projections of the optical fibers projecting from the sandwiching portion of the V-groove and the lid plate, and the adhesive is infiltrated into the sandwiching portion by a surface tension of the adhesive. Thereafter, the adhesive is cured, and the optical fibers are fixed to the V-groove substrate. Then, the projections of the optical fibers are removed, and the end surfaces of the optical fiber are aligned with the end surface of the V-groove substrate.
Recently, however, further increase in the density of the optical fiber array is required. For example, it is required that a substrate is formed such that the average value of pitches of maximum 48 grooves becomes substantially equal to an outer diameter “d” of the optical fibers (in a range of 1.0 times to 1.1 times of “d”), and optical fibers are mounted on the substrate to form the optical fiber array. The pitch of the grooves means a distance between adjacent V-grooves, and the average value of the pitches of the grooves means the average value of a plurality of grooves formed on one substrate.
An attempt is made to produce such an optical fiber array using a conventional method, according to Japanese Patent Application Laid-open No. 2005-181724. However, there are sometimes difficulties in assembling the members, and even when the members can be assembled excellently, insertion loss with a PLC (Planar Lightwave Circuit) is increased in some cases.
This is because in the conventional optical fiber array, attention is paid only on the management of size precision of the V-groove substrate and the lid, and no attention is paid to the geometric parameters of the “optical fiber” itself which is a constituent part of the optical fiber array together with the V-groove substrate and the lid. For example, even if an optical fiber is specified with an outer diameter as “125 μm”, the numeric value of 125 μm is a nominal value, and in an actual case, optical fibers have various outer diameters in a range of 124 μm to 126 μm as described in JIS (Japanese Industrial Standards)_C6835. Therefore, even if the size precisions of the V-groove substrate and the lid are managed in submicron unit, if the geometric parameters of the optical fiber itself is not managed precisely, desired transmission characteristics of the optical fiber array cannot be achieved.